1. Technical Field
The present invention specifically relates to an optical recording medium in which information can be recorded by a hologram and information can be reproduced by an irradiating beam, and a method of manufacturing the same.
2. Description of the Related Art
A holographic data storage is a memory for recording information in a recording medium using holographic technology by overlapping a signal beam having image information and a reference beam in the interior of the recording medium and writing interference patterns generated at this time in the recording medium. The recorded information is read by irradiating the reference beam to the recording medium and obtaining the image information from diffraction caused by the interference patterns.
U.S. Pat. No. 5,698,344 discloses a holographic data storage and a holographic recording/reproducing medium for recording and reproducing information with respect thereto. In the holographic data storage, since the interference patterns are three-dimensionally written using the thickness of the recording medium, selectivity of the wavelength and the angle of beam is high, and hence multiplexing is enabled and high recording capacity is achieved. Since the image information can be read by one shot, it has an advantage such that the transfer rate of reproduced signals is high.
The image information to be recorded is generally encoded digital information. In order to reproduce, the recorded image information is reproduced and decoded to take out as information.
What is essential to be developed to achieve such a recording is a medium having a thick recording layer in which the interference patterns can be recorded three-dimensionally as described in JP-2001-5368.
The most-used photopolymer as a medium of the holographic data storage achieves recording by generating a density distribution, so that the volume of the recording layer is reduced by recording. When the ratio of volume reduction of the photopolymer is high, the method of reproduction must be thought out. For example, reproduction may be achieved by varying the angle of a disk with respect to reproducing beam or varying the position of a detector for the reproducing beam in the case of off-axis holographic recording, and by varying conversion conditions (e.g., decoding condition) of the intensity of the reproducing beam detected by the detector in the case of a coaxial holographic data recording.
When manufacturing the medium, there arises a problem such that the recording surface area on the medium is reduced in association with volume reduction of a precursor substance when solution as the precursor substance of the recording layer is cured.
In addition, recording characteristics of the photopolymer are deleteriously affected by oxygen or water in many cases. When the recording material can be isolated from oxygen or water, recording with higher density can be realized.